Date:   Wed, 19 Feb 2020 09:46:46 +0100
From:   Jessica Yu <jeyu@...nel.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Matthias Maennich <maennich@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Martijn Coenen <maco@...roid.com>
Subject: Re: [PATCH] modpost: return error if module is missing ns imports
 and MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS=n

+++ Masahiro Yamada [19/02/20 04:27 +0900]:
>On Wed, Feb 19, 2020 at 1:06 AM Jessica Yu <jeyu@...nel.org> wrote:
>>
>> +++ Matthias Maennich [17/02/20 14:56 +0000]:
>> >Hi Jessica!
>> >
>> >On Fri, Feb 14, 2020 at 03:37:09PM +0100, Jessica Yu wrote:
>> >>Currently when CONFIG_MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS=n, modpost only warns
>> >>when a module is missing namespace imports. Under this configuration, such a module
>> >>cannot be loaded into the kernel anyway, as the module loader would reject it.
>> >>We might as well return a build error when a module is missing namespace imports
>> >>under CONFIG_MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS=n, so that the build
>> >>warning does not go ignored/unnoticed.
>> >
>> >I generally agree with the idea of the patch. Thanks for working on
>> >this! I also can't remember any reason why I did not write it like this
>> >initially. Probably just because I introduced this configuration option
>> >quite late in the development process of the initial patches.
>> >
>> >>
>> >>Signed-off-by: Jessica Yu <jeyu@...nel.org>
>> >>---
>> >>scripts/Makefile.modpost |  1 +
>> >>scripts/mod/modpost.c    | 19 +++++++++++++++----
>> >>2 files changed, 16 insertions(+), 4 deletions(-)
>> >>
>> >>diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
>> >>index b4d3f2d122ac..a53660f910a9 100644
>> >>--- a/scripts/Makefile.modpost
>> >>+++ b/scripts/Makefile.modpost
>> >>@@ -53,6 +53,7 @@ MODPOST = scripts/mod/modpost                                               \
>> >>      $(if $(KBUILD_EXTMOD),$(addprefix -e ,$(KBUILD_EXTRA_SYMBOLS))) \
>> >>      $(if $(KBUILD_EXTMOD),-o $(modulesymfile))                      \
>> >>      $(if $(CONFIG_SECTION_MISMATCH_WARN_ONLY),,-E)                  \
>> >>+     $(if $(CONFIG_MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS),,-N)      \
>> >>      $(if $(KBUILD_MODPOST_WARN),-w)
>> >>
>> >>ifdef MODPOST_VMLINUX
>> >>diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
>> >>index 7edfdb2f4497..53e966f7d557 100644
>> >>--- a/scripts/mod/modpost.c
>> >>+++ b/scripts/mod/modpost.c
>> >>@@ -39,6 +39,8 @@ static int sec_mismatch_count = 0;
>> >>static int sec_mismatch_fatal = 0;
>> >>/* ignore missing files */
>> >>static int ignore_missing_files;
>> >>+/* Return an error when there are missing namespace imports */
>> >>+static int missing_ns_import_error = 0;
>> >
>> >A more suitable name is maybe missing_ns_import_is_error or follow the
>> >naming of the config option: allow_missing_ns_imports (with default = 1).
>> >
>> >>
>> >>enum export {
>> >>      export_plain,      export_unused,     export_gpl,
>> >>@@ -2216,9 +2218,15 @@ static int check_exports(struct module *mod)
>> >>
>> >>              if (exp->namespace &&
>> >>                  !module_imports_namespace(mod, exp->namespace)) {
>> >>-                     warn("module %s uses symbol %s from namespace %s, but does not import it.\n",
>> >>-                          basename, exp->name, exp->namespace);
>> >>-                     add_namespace(&mod->missing_namespaces, exp->namespace);
>> >>+                     if (missing_ns_import_error) {
>> >>+                             merror("module %s uses symbol %s from namespace %s, but does not import it.\n",
>> >>+                                     basename, exp->name, exp->namespace);
>> >
>> >I would like to avoid the code duplication here. The string literal is
>> >identical for both cases.
>>
>> Hm, but one is a call to merror() and the other to warn(). The
>> previous if (warn_unresolved) block does the same thing. I am not sure
>> how to simplify it to one call without introducing macro magic or
>> overcomplicating things. Or were you thinking of something else?
>
>
>I would not say this is a horrible duplication,
>but if you avoid repeating the same string,
>maybe you could do like this:
>
>PRINTF log(enum loglevel loglevel, const char *fmt, ...)
>
>
>
>BTW, you accidentally changed the indentation of
>add_namespace(&mod->missing_namespaces, exp->namespace);
>
>
>
>> >>+                             err = 1;
>> >
>> >Also, if we fail here, we might as well help the user to fix it by
>> >suggesting to run `make nsdeps` (once per failed modpost run). Speaking
>> >of which, `make nsdeps` is currently broken by this patch as it relies
>> >on a successful (yet warning-full) build of the modules. So, in case of
>> >`make nsdeps`, we probably have to omit the -N flag again when invoking
>> >modpost.
>>
>> Good catch! Since KBUILD_NSDEPS is set when running `make nsdeps`,
>> maybe we can do something like:
>>
>> diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
>> index a53660f910a9..145703ef8d3a 100644
>> --- a/scripts/Makefile.modpost
>> +++ b/scripts/Makefile.modpost
>> @@ -53,7 +53,7 @@ MODPOST = scripts/mod/modpost                                         \
>>         $(if $(KBUILD_EXTMOD),$(addprefix -e ,$(KBUILD_EXTRA_SYMBOLS))) \
>>         $(if $(KBUILD_EXTMOD),-o $(modulesymfile))                      \
>>         $(if $(CONFIG_SECTION_MISMATCH_WARN_ONLY),,-E)                  \
>> -       $(if $(CONFIG_MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS),,-N)      \
>> +       $(if $(CONFIG_MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS),,$(if $(KBUILD_NSDEPS),,-N))      \
>
>
>If you follow Matthias' suggestion
>"follow the naming of the config option: allow_missing_ns_imports
>(with default = 1)."
>the option is inverted, and you can write it more simply:
>
>
>      $(if $(CONFIG_MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS)$(KBUILD_NSDEPS),-n)
>     \

Yeah, that looks much better. Thanks!

Jessica

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